Typically an elevator comprises an elevator car and a hoisting machine configured to drive the elevator car in an elevator shaft between landings. When the elevator car is arriving to a landing, the elevator car is instructed to decelerate and finally to stop to the landing. To improve the accuracy of stopping the elevator car at the landing a levelling operation is used.
During the levelling operation the elevator car is allowed to move with open door(s) at an unlocking zone. However, the levelling speed of the elevator car is limited within the unlocking zone. The unlocking zone is typically defined as a zone extending from above and below a floor level of the landing, in which the elevator car floor must be in order to enable the door(s) to be unlocked. Both the car door(s) and landing door(s) may be unlocked during the levelling operation at the unlocking zone. The speed of the elevator car is also limited during a re-levelling of the elevator car. The re-levelling is an operation that is performed after the elevator car is stopped, to allow the stopping position of the elevator car to be corrected during loading or unloading, if necessary.
The speed limits for levelling and re-levelling are defined by standards. For example in EN 81-1 and EN 81-20 the speed limit for levelling with door(s) open is 0.8 m/s and for re-levelling with door(s) open is 0.3 m/s. According to another example in A17.1 standard the speed limit for levelling and re-levelling with door(s) open is 0.75 m/s. Furthermore, according to Unintended Car Movement Protection (UCMP) requirement the elevator car shall be stopped within a predetermined distance from the landing, if the elevator car moves away from the unlocking zone with open door(s).
According to prior art solutions, a fixed levelling speed limit value is set for the elevator car. If the speed of the elevator car meets the fixed levelling speed limit value during the levelling operation, the speed of the elevator car is configured figured to be decelerated or the movement of the elevator car is configured to be stopped.
However, one drawback of the prior art solution is that the stopping of the elevator car within the predetermined distance from the landing may be challenging or even impossible. Especially, if the elevator car moves away from the landing and leaves the unlocking zone at a speed that is close to the levelling speed limit. Thus, the higher the levelling speed limit is the longer the time to react to an unusual movement of the elevator car is.
Hence, there is a need to develop further solutions in order to mitigate the described drawbacks at least partly.